Amid rising concerns over the impact on WiFi of the planned LTE expansion into unli-censed spectrum, the WiFi Alliance has published its first guidelines specifying testing for coexistence without performance impairment.
However, after its Coexistence Test Workshop, held early in Novembe, the Alliance con-firmed that more work was needed to establish a full testing framework that would en-sure LTE-Unlicensed does not affect WiFi performance in any use case or deployment sce-nario, including premium video.
The LTE-U standard is just one of the ways in which LTE is being adapted to run in the li-cence-exempt 5 GHz band (or potentially others). It is already part of the 3GPP standards, but can only be supported in certain markets, notably the US, which do not insist on ‘listen before talk’ mechanisms to avoid interference in 5 GHz. A version with LBT support, LTE-LAA, will be part of the Release 13 standards, but will not be ratified until next year, nor fully commercialized until 2016 (though some operators may deploy pre-standard imple-mentations).
For now, then, the WiFi community’s fears that LTE may interfere with their services and/or hijack their business model are focused most urgently on LTE-U because it could be de-ployed in a short timeframe in the world’s second largest market, if it succeeds in per-suading the FCC that it will be a good neighbor.
The specifications have been modified to allay WiFi fears and Edgar Figueora, the WiFi Alliance’s CEO, says these changes have addressed some of the concerns relating to ambi-guity of the LTE-U specifications, which have made the impact on WiFi be hard to assess.
“A number of updates to the LTE-U specification were presented at the workshop, which we believe to be a good step toward addressing some of these concerns,” said Figueroa last month. “We reached consensus on a number of points, including agreement that more specificity improves the LTE-U specification and a broader set of test scenarios will be necessary to ensure fairness.”
The WiFi Alliance has realized that the current set of testing guidelines is just a first ver-sion that will need to be extended. “There is broad interest in collaborating on the work to establish the testing that will be required,” said Figueroa. This sets the stage for a more cooperative approach to development of WiFi/LTE-U coexistence than has been the case so far, but continued harmony will depend on the outcome of future tests. The first guide-lines set out the stall for establishing the impact of coexistence on key use cases as deter-mined by measurements of the usual parameters, including file transfer time, packet loss, latency and jitter.
Initial test guidelines:
We should note that the WiFi community accepts the reality of LTE-U and its intrusion in-to its domain, but insists that it should operate just like a WiFi network and share similar characteristics. The purpose of the testing therefore is to demonstrate that the impact of an LTE-U network on an adjacent or overlapping WiFi network is no worse than that of a second WiFi network.
For this reason, the test guidelines stipulate comparison between two tests, one with two coexisting WiFi networks as a control, and then one running a WiFi network alongside an LTE-U network, in both cases in the same physical space.
The aim here is to establish a common basis for future WiFi/LTE coexistence studies which will, in turn, help build a coherent scheme for testing unlicensed LTE deployments.
This boils down to three specific objectives. The first is to identify appropriate key perfor-mance indicators (KPIs) that characterize the performance of different traffic profiles and then specify how the KPIs should be measured and presented.
Second is to define the topologies or configurations of both the WiFi and LTE networks to be studied, including number of devices and their positioning within the physical network, along with some other physical characteristics of the setup such as perhaps device types. The third is to define clearly the type and mix of data traffic loading the network under study, to enable meaningful comparisons between test results.
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